HR: 1340h
AN: G13A-0912    [Abstracts]
TI: Spatial resolution of afterslip following the 2004 M6 Parkfield earthquake
AU: * Murray-Moraleda, J R
EM: jrmurray@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, United States
AU: Simpson, R
EM: simpson@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, United States
AU: Langbein, J
EM: langbein@usgs.gov
AF: U. S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, United States
AB: A strong postseismic deformation signal was recorded by creepmeters and continuous GPS stations starting in the minutes to hours following the 2004 M6 Parkfield earthquake. Several studies have shown that the observed displacements were likely due to afterslip (aseismic slip due to coseismic stress changes), and the estimated moment release of this postseismic slip was anomalously large, exceeding the coseismic moment. Information regarding the spatio-temporal progression of afterslip has the potential to shed light on the underlying processes that give rise to postseismic deformation and aftershocks, as well as fault frictional properties. Preliminary results from a time-dependent inversion of Global Positioning System (GPS) data recorded at 14 continuously-operating and 13 survey-mode GPS receivers during the first 60 days of the postseismic period suggest that afterslip began at shallow depths but spread deeper and surrounded the region of peak coseismic slip estimated from geodetic data. The degree to which these results may be used to address questions relating to underlying processes depends on the degree to which features of the imaged slip distribution are well-resolved. Through a series of simulations and assessments of model resolution we have explored the extent to which it is possible to accurately recover the spatial distribution of slip at depth given the available station coverage at Parkfield. Resolution of slip at depth is known to be poor, and our results confirm that below 6 km slip cannot be reliably imaged. We applied these findings to construct a model fault geometry, comprised of variably-sized subfaults, that better reflects the resolving power of the data and lessens the computational burden by reducing the number of model parameters. Using the revised fault geometry in time-dependent modeling of the spatio-temporal evolution of afterslip, we can more realistically assess which features of the imaged slip history are robust and what insights into underlying processes the GPS data provide.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
SC: Geodesy [G]
MN: 2007 Fall Meeting